Hybrid drill bit and method of using tsp or mosaic cutters on a hybrid bit

ABSTRACT

An earth boring drill bit comprising: a bit body; a plurality of fixed blades extending downwardly from the bit body, each blade having a leading edge; a plurality of fixed-blade cutting elements arranged on the leading edge of the fixed blades; at least one rolling cutter mounted for rotation on the bit body; and wherein the rolling cutter is configured to act as a depth-of-cut limiter, thereby reducing the risk of damage to the fixed-blade cutting elements. The fixed-blade cutting elements may include thermally stable polycrystalline diamond wafers mounted on tungsten carbide substrates and/or a mosaic of geometrically-shaped thermally stable diamond elements cooperatively arranged and bonded to form a unitary cutting surface. The rolling cutter may be positioned, relative to the fixed blades, to also limit rate of penetration and/or exposure of the fixed-blade cutting elements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/061,536, filed Apr. 2, 2008 and entitled “Hybrid Drill Bit and Methodof Drilling”, which is a continuation-in-part of U.S. application Ser.No. 11/784,025, filed Apr. 5, 2007 and entitled “Fixed Cutters as theSole Cutting Elements in the Axial Center of the Drill Bit”. Both ofthese applications are incorporated herein by specific reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The inventions disclosed and taught herein relate generally toearth-boring drill bits; and more specifically relate to a bit having acombination of rolling and fixed cutters and a method of using TSPand/or Mosaic cutters on such a bit.

2. Description of the Related Art

In the prior art, some earth-boring bits use a combination of one ormore rolling cutters and one or more fixed blades. Some of thesecombination-type drill bits are referred to as hybrid bits. Previousdesigns of hybrid bits, such as is described in U.S. Pat. No. 4,343,371,to Baker, III, have provided for the rolling cutters to do most of theformation cutting, especially in the center of the hole or bit. Othertypes of combination bits are known as “core bits,” such as U.S. Pat.No. 4,006,788, to Garner. Core bits typically have truncated rollingcutters that do not extend to the center of the bit and are designed toremove a core sample of formation by drilling down, but around, a solidcylinder of the formation to be removed from the borehole generallyintact.

Another type of hybrid bit is described in U.S. Pat. No. 5,695,019, toShamburger, Jr., wherein the rolling cutters extend almost entirely tothe center. Fixed cutter inserts 50 (FIGS. 2 and 3) are located in thedome area 2 or “crotch” of the bit to complete the removal of thedrilled formation. Still another type of hybrid bit is sometimesreferred to as a “hole opener,” an example of which is described in U.S.Pat. No. 6,527,066. A hole opener has a fixed threaded protuberance thatextends axially beyond the rolling cutters for the attachment of a pilotbit that can be a rolling cutter or fixed cutter bit. In these lattertwo cases the center is cut with fixed cutter elements but the fixedcutter elements do not form a continuous, uninterrupted cutting profilefrom the center to the perimeter of the bit.

U.S. Pat. No. 4,006,788 discloses a “rock bit for recovering coresamples is described, along with variations for drilling oil wells orthe like. In each of these embodiments a plurality of diamond cuttersare mounted on the bit body for cutting rock by a shearing action. Eachdiamond cutter is in the form of a thin diamond plate bonded to acarbide slug that is inserted into the bit body. Means are also providedfor limiting the depth of penetration of the diamond cutters into therock formation being drilled preferably in the form of rolling conecutters having a plurality of carbide insects protruding from theirsurfaces. The protrusion of the carbide inserts from the surface of thecutter cones is less than the length of the diamond plate. This limitsthe depth that the diamond can penetrate in the rock and inhibitsdamage. Typically the diamond cutters are mounted for cutting oneportion of the hole area by shearing action and the rolling cone cuttersare mounted for cutting another portion of its area by chipping-crushingaction.”

U.S. Pat. No. 4,285,409 discloses a “hybrid rock bit is disclosed whichconsists of a pair of cone cutters mounted to legs 120.degree. apartwith an extended drag bit leg occupying the remaining 120.degree.segment. Several synthetic diamond stand-off type studs arestrategically located and inserted in insert holes formed in the face ofthe drag bit leg. Nozzles are placed in front of the cutting face of thediamond studs to cool and clean the studs as the bit works in aborehole.”

U.S. Pat. No. 4,343,371 discloses a “hybrid rock bit is disclosedwherein a pair of opposing extended nozzle drag bit legs are positionedadjacent a pair of opposed tungsten carbide roller cones. The extendednozzle face nearest the hole bottom has a multiplicity of diamondinserts mounted therein. The diamond inserts are strategicallypositioned to remove the ridges between the kerf rows in the hole bottomformed by the inserts in the roller cones.”

U.S. Pat. No. 4,444,281 discloses a “rotary drill bit comprising a bitbody having at least one depending leg at its lower end and at least oneroller cutter rotatably mounted on the leg. The roller cutter comprisesa frustoconical roller cutter body and a plurality of cutting elementsprojecting from the cutter body to tips adapted to bear on the bottom ofthe well bore, with the tips defining, upon rotation of the bit, a firstcutting surface of the bit extending over substantially the entire areaof the bottom of the well bore. At least one drag cutter extends downfrom the bit body and comprises a support and a plurality of dragcutting elements on the support, each having a lower cutting edge. Thecutting edges of these elements are so arranged relative to the tips ofthe hard metal cutting elements as to define, upon rotation of the bit,a second cutting surface of generally the same configuration as thefirst but spaced above it, whereby upon drilling a relatively brittleformation only the hard metal cutting elements bear on the formation forcutting the formation by fracturing it thereby protecting the dragcutting elements, and upon drilling a relatively plastically deformablematerial which the hard metal cutting elements penetrate to a relativelydeep depth without causing substantial fracturing of the formation, thedrag cutting elements also engage the formation for improved drill bitcutting action and increased rates of drilling penetration.”

U.S. Pat. No. 4,726,718 discloses a “diamond cutter for use in a drillbit having a geometric size and shape normally characterized byunleached diamond product, such as STRATAPAX diamond cutters, can befabricated by assembling a plurality of prefabricated leachedpolycrystalline diamond (PCD) elements in an array in a cutting slug. Acutting slug is formed of matrix material which in one embodiment isimpregnated with diamond grit. The cutting face of the cutting slug ischaracterized by exposing at least one surface of each of the PCDelements disposed therein. The diamonds may be set within the cuttingslug either in a compact touching array or in a spaced-apartrelationship. More than one type of array may also be employed within asingle cutting slug. The PCD elements can assume a variety of polyhedralshapes such as triangular prismatic elements, rectangular elements,hexagonal elements and the like. The plurality of diamond elements andthe cutting slug are fabricated using hot pressing or infiltrationtechniques.”

U.S. Pat. No. 4,943,488 discloses an “improved temperature stablesynthetic polycrystalline diamond (PCD) product includes at least onetemperature stable PCD integrally and chemically bonded to a matrixcarrier support through a carbide forming layer which is of a thicknessof at least about 1 micron, the layer on at least one surface of the PCDis in turn bonded to the matrix carrier. A wide variety of shapes, sizesand configurations of such products is achieved through relatively lowtemperature and relatively low pressure processing. Various products ofvarious geometries are described as well as the details of theprocessing to achieve chemical bonding of the PCD elements in a varietyof support matrix carrier materials to form a unitary structure having atemperature stability up to about 1,200 degrees C.”

U.S. Pat. No. 5,027,912 discloses drill bits that “may include cuttingmembers which have cutting faces formed of segments of differing cuttingmaterials. The faces of the cutting members may include two or moresegments, with the segments formed from at least two differentmaterials. For example, a first segment could be formed of apolycrystalline diamond compact surface while a second segment could beformed of a thermally stable diamond product material.”

U.S. Pat. No. 5,028,177 discloses a “diamond cutter for use in a drillbit having a geometric size and shape normally characterized byunleached diamond product, such as STRATAPAX diamond cutters, can befabricated by assembling a plurality of prefabricated leachedpolycrystalline diamond (PCD) elements in an array in a cutting slug. Acutting slug is formed of matrix material which in one embodiment isimpregnated with diamond grit. The cutting face of the cutting slug ischaracterized by exposing at least one surface of each of the PCDelements disposed therein. The diamonds may be set within the cuttingslug either in a compact touching array or in a spaced-apartrelationship. More than one type of array may also be employed within asingle cutting slug. The PCD elements can assume a variety of polyhedralshapes such as triangular prismatic elements, rectangular elements,hexagonal elements and the like. The plurality of diamond elements andthe cutting slug are fabricated using hot pressing or infiltrationtechniques.”

U.S. Pat. No. 5,030,276 discloses an “improved temperature stablesynthetic polycrystalline diamond (PCD) product includes at least onetemperature stable PCD integrally and chemically bonded to a matrixcarrier support through a carbide forming layer which is of a thicknessof at least about 1 micron, the layer on at least one surface of the PCDis in turn bonded to the matrix carrier. A wide variety of shapes, sizesand configurations of such products is achieved through relatively lowtemperature and relatively low pressure processing. Various products ofvarious geometries are described as well as the details of theprocessing to achieve chemical bonding of the PCD elements in a varietyof support matrix carrier materials to form a unitary structure having atemperature stability up to about 1,200 degrees C.”

U.S. Pat. No. 5,116,568 discloses an “improved temperature stablesynthetic polycrystalline diamond (PCD) product includes at least onetemperature stable PCD integrally and chemically bonded to a matrixcarrier support through a carbide forming layer which is of a thicknessof at least about 1 micron, the layer on at least one surface of the PCDis in turn is bonded to the matrix carrier. A wide variety of shapes,sizes and configurations of such products is achieved through relativelylow temperature and relatively low pressure processing. Various productsof various geometries are described as well as the details of theprocessing to achieve chemical bonding of the PCD elements in a varietyof support matrix carrier materials to form a unitary structure having atemperature stability up to about 1,200 degrees C.”

U.S. Pat. No. 5,238,074 discloses a “cutter for a rotating drag bitwhich has a cutting face formed from a plurality of polycrystallinediamond compact (PCD) elements. The elements can be of varying thicknessand/or varying hardness to provide a cutting edge having a nonuniformwear pattern. Also provided is a cutter which includes two layers of PCDelements. The PCD elements can be of varying thickness and/or hardnessto provide a cutter which presents a cutting edge having a wear ratiowhich varies with cutter wear. Also provided is an impact cutter havinga cutting surface formed from one or more layers of PCD elements.”

European Patent No. EP157278 discloses a “diamond cutting table havingthe geometric characteristics of larger unleached diamond compactproducts and yet characterised by the physical properties of smallerleached diamond products is fabricated by forming a diamond cutterincorporating a plurality of polycrystalline diamond (PCD) leached disks(12). The PCD leached disks (12) are disposed in array in a cutting slug(10) formed of matrix material (14). The matrix material is disposedbetween and around the plurality of diamond disks (12) and in oneembodiment incorporates a volume distribution of diamond grit. Thecutting slug is hot pressed or infiltrated to form an integral mass ortable. The diamond table is then bonded to a cutter or directly moldedinto an integral tooth within a matrix body bit.”

European Patent No. EP225101 discloses a “rotary drill bit for drillingdeep holes in subsurface formations comprises a bit body (10) having ashank for connection to a drill string and a plurality of elements(16,22) mounted on the bit body (10) for cutting, abrading or bearing onthe formation being drilled. The bit body (10) includes a fixedstructure (11) and a movable structure (17), each carrying elements(16,22) for acting on the formation, the movable structure (17) beingcapable of reversible movement relatively to the fixed structure (11)between two limiting positions, the relative movement providing at leasttwo configurations in which there are different distributions, betweensaid elements (16,22), of the loads applied to the bit during itsengagement with the formation. Control means, such as hydraulic means(29,30), are provided to control the movement of the movable structure(17), and hence the load distribution between the elements (16,22),automatically in response to the torque and/or axial loads applied tothe bit.”

United Kingdom Patent Application No. GB 2183694 discloses a “rotarydrill bit for drilling deep holes in subsurface formations comprises abit body 10 having a shank 14 for connection to a drill string and aplurality of elements 22,16 mounted on the bit body for cutting,abrading or bearing on the formation being drilled. The bit bodyincludes a fixed structure 11 and a movable structure 17, each carryingelements for acting on the formation, the movable structure beingcapable of reversible movement relatively to the fixed structure betweentwo limiting positions, the relative movement providing at least twoconfigurations in which there are different distributions, between saidelements 22,16, of the loads applied to the bit during its engagementwith the formation. Control means, such as hydraulic means 29,30 orspring means, are provided to control the movement of the movablestructure 17, and hence the load distribution between the elements22,16, automatically in response to the torque and/or axial loadsapplied to the bit.”

The inventions disclosed and taught herein are directed to an improveddrill bit having a combination of rolling and fixed cutters and a methodof using TSP and/or Mosaic cutters on such a bit.

BRIEF SUMMARY OF THE INVENTION

An earth boring drill bit comprising: a bit body; a plurality of fixedblades extending downwardly from the bit body, each blade having aleading edge and a trailing edge; a plurality of fixed-blade cuttingelements arranged on the leading edge of the fixed blades; at least onerolling cutter mounted for rotation on the bit body; and wherein therolling cutter is configured to act as a depth-of-cut limiter, therebyreducing the risk of damage to the fixed-blade cutting elements. Thefixed-blade cutting elements may include thermally stablepolycrystalline diamond wafers mounted on tungsten carbide substratesand/or a mosaic of geometrically-shaped thermally stable diamondelements cooperatively arranged and bonded to form a unitary cuttingsurface. The rolling cutter may be positioned, relative to the fixedblades, such that any rolling-cutter cutting elements and thefixed-blade cutting elements cooperate up to a maximum depth-of-cut. Therolling cutter may be positioned, relative to the fixed blades, to limitdepth-of-cut, rate of penetration, and/or exposure of the fixed-bladecutting elements. The rolling cutter may be positioned, relative to thefixed blades, such that any rolling-cutter cutting elements extendbeyond the fixed blades and/or the fixed-blade cutting elements. Therolling cutter may be aligned with the fixed-blade cutting elements orbetween the fixed blades and the fixed-blade cutting elements.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a bottom plan view of an embodiment of the hybridearth-boring bit constructed in accordance with certain aspects of thepresent inventions;

FIG. 2 illustrates a side elevation view of the embodiment of the hybridearth-boring bit of FIG. 1 constructed in accordance with certainaspects of the present inventions;

FIG. 3 illustrates a side elevation view of the hybrid earth-boring bitof FIG. 1 constructed in accordance with certain aspects of the presentinventions;

FIG. 4 illustrates a bottom plan view of the embodiment of the hybridearth-boring bit of FIGS. 1 through 3 showing streams of fluid directedfrom the nozzles;

FIG. 5 illustrates a side elevation view of the embodiment of the hybridearth-boring bit of FIGS. 1 through 3 showing streams of fluid directedfrom the nozzles;

FIG. 6 illustrates a first side elevation view of the rolling cuttersemployed in the embodiment of the hybrid earth-boring bit of FIGS. 1through 3;

FIG. 7 illustrates a second side elevation view of the rolling cuttersemployed in the embodiment of the hybrid earth-boring bit of FIGS. 1through 3;

FIG. 8 illustrates a composite view of all of the rolling-cutter cuttingelements and the fixed-blade cutting elements on the embodiment of thehybrid drill bit of FIGS. 1 through 3 rotated about the central axis ofthe bit body and into one plane, and commonly known as a “cuttingprofile”;

FIG. 9 illustrates a superimposition of the cutting profile of FIG. 8onto a cutting profile of a typical rolling-cutter earth-boring bit; and

FIG. 10 illustrates a side elevation view of another embodiment of thehybrid earth-boring bit constructed in accordance with certain aspectsof the present inventions.

DETAILED DESCRIPTION OF THE INVENTION

The Figures described above and the written description of specificstructures and functions below are not presented to limit the scope ofwhat Applicants have invented or the scope of the appended claims.Rather, the Figures and written description are provided to teach anyperson skilled in the art to make and use the inventions for whichpatent protection is sought. Those skilled in the art will appreciatethat not all features of a commercial embodiment of the inventions aredescribed or shown for the sake of clarity and understanding. Persons ofskill in this art will also appreciate that the development of an actualcommercial embodiment incorporating aspects of the present inventionswill require numerous implementation-specific decisions to achieve thedeveloper's ultimate goal for the commercial embodiment. Suchimplementation-specific decisions may include, and likely are notlimited to, compliance with system-related, business-related,government-related and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time-consuming in an absolute sense, suchefforts would be, nevertheless, a routine undertaking for those of skillin this art having benefit of this disclosure. It must be understoodthat the inventions disclosed and taught herein are susceptible tonumerous and various modifications and alternative forms. Lastly, theuse of a singular term, such as, but not limited to, “a,” is notintended as limiting of the number of items. Also, the use of relationalterms, such as, but not limited to, “top,” “bottom,” “left,” “right,”“upper,” “lower,” “down,” “up,” “side,” and the like are used in thewritten description for clarity in specific reference to the Figures andare not intended to limit the scope of the invention or the appendedclaims.

Applicants have created an earth boring drill bit comprising: a bitbody; a plurality of fixed blades extending downwardly from the bitbody, each blade having a leading edge and a trailing edge; a pluralityof fixed-blade cutting elements arranged on the leading edge of thefixed blades; at least one rolling cutter mounted for rotation on thebit body; and wherein the rolling cutter is configured to act as adepth-of-cut limiter, thereby reducing the risk of damage to thefixed-blade cutting elements. The fixed-blade cutting elements mayinclude thermally stable polycrystalline diamond wafers mounted ontungsten carbide substrates and/or a mosaic of geometrically-shapedthermally stable diamond elements cooperatively arranged and bonded toform a unitary cutting surface. The rolling cutter may be positioned,relative to the fixed blades, such that any rolling-cutter cuttingelements and the fixed-blade cutting elements cooperate up to a maximumdepth-of-cut. The rolling cutter may be positioned, relative to thefixed blades, to limit depth-of-cut, rate of penetration, and/orexposure of the fixed-blade cutting elements. The rolling cutter may bepositioned, relative to the fixed blades, such that any rolling-cuttercutting elements extend beyond the fixed blades and/or the fixed-bladecutting elements. The rolling cutter may be aligned with the fixed-bladecutting elements or between the fixed blades and the fixed-blade cuttingelements.

Referring to FIGS. 1-8, an earth-boring bit 11 according to anembodiment of the present invention is disclosed. Bit 11 comprises a bitbody 13 having a central longitudinal axis 15 that defines an axialcenter of the bit body 13. In the illustrated embodiment, the bit body13 is steel, but could also be formed of matrix material with steelreinforcements, or of a sintered carbide material. Bit body 13 includesa shank at the upper or trailing end thereof threaded or otherwiseconfigured for attachment to a hollow drillstring (not shown), whichrotates bit 11 and provides pressurized drilling fluid to the bit andthe formation being drilled.

The radially outermost surface of the bit body 13 is known as the gagesurface and corresponds to the gage or diameter of the borehole (shownin phantom in FIG. 1) drilled by bit 11. At least one (two are shown)bit leg 17 extends downwardly from the bit body 13 in the axialdirection. The bit body 13 also has a plurality (e.g., also two shown)of fixed blades 19 that extend downwardly in the axial direction. Thenumber of bit legs 17 and fixed blades 19 is at least one but may bemore than two. In the illustrated embodiment, bit legs 17 (and theassociated rolling cutters) are not directly opposite one another (areabout 191 degrees apart measured in the direction of rotation of bit11), nor are fixed blades 19 (which are about 169 degrees apart measuredin the direction of rotation of bit 11). Other spacings anddistributions of legs 17 and blades 19 may be appropriate.

A rolling cutter 21 is mounted on a sealed journal bearing that is partof each bit leg 17. According to the illustrated embodiment, therotational axis of each rolling cutter 21 intersects the axial center 15of the bit 11. Sealed or unsealed journal or rolling-element bearingsmay be employed as cutter bearings. Each of the rolling cutters 21 isformed and dimensioned such that the radially innermost ends of therolling cutters 21 are radially spaced apart from the axial center 15(FIG. 1) by a minimal radial distance 23 of about 0.60 inch. As shown inparticular in FIGS. 6 and 7, rolling cutters 21 are not conical inconfiguration as is typical in conventional rolling cutter bits.Further, the radially outermost surface of each rolling cutter 21(typically called the gage cutter surface in conventional rolling cutterbits), as well as the bit legs 17, are “off gage” or spaced inward fromthe outermost gage surface of bit body 13. In the illustratedembodiment, rolling cutters 21 have no skew or angle and no offset, sothat the axis of rotation of each rolling cutter 21 intersects the axialcenter (central axis) 15 of the bit body 13 (as shown in FIG. 8).Alternatively, the rolling cutters 21 may be provided with skew angleand (or) offset to induce sliding of the rolling cutters 21 as they rollover the borehole bottom. In some embodiments, the rolling cutters 21may be constructed from cast carbide, hard faced steel, or some othertype of plain metal.

At least one (a plurality are illustrated) rolling-cutter cuttinginserts or elements 25 are arranged on the rolling cutters 21 ingenerally circumferential rows thereabout such that each cutting element25 is radially spaced apart from the axial center 15 by a minimal radialdistance 27 of about 0.30 inch. The minimal radial distances 23, 27 mayvary according to the application and bit size, and may vary from coneto cone, and/or cutting element to cutting element, an objective beingto leave removal of formation material at the center of the borehole tothe fixed-blade cutting elements 31 (rather than the rolling-cuttercutting elements 25). Rolling-cutter cutting elements 25 need not bearranged in rows, but instead could be “randomly” placed on each rollingcutter 21. Moreover, the rolling-cutter cutting elements may take theform of one or more discs or “kerf-rings,” which would also fall withinthe meaning of the term rolling-cutter cutting elements.

Tungsten carbide inserts, secured by interference fit into bores in therolling cutter 21 are shown, but a milled- or steel-tooth cutter havinghardfaced cutting elements (25) integrally formed with and protrudingfrom the rolling cutter could be used in certain applications and theterm “rolling-cutter cutting elements” as used herein encompasses suchteeth. The inserts or cutting elements may be chisel-shaped as shown,conical, round, or ovoid, or other shapes and combinations of shapesdepending upon the application. Rolling-cutter cutting elements 25 mayalso be formed of, or coated with, superabrasive or super-hard materialssuch as polycrystalline diamond, cubic boron nitride, and the like. Thebit 11 may include one or more rolling cutters 21, without or withoutrolling-cutter cutting elements 25, preferably with one rolling cutter21 mounted on each bit leg 17.

In addition, a plurality of fixed or fixed-blade cutting elements 31 arearranged in a row and secured to each of the fixed blades 19 at theleading edges thereof (leading being defined in the direction ofrotation of bit 11). Each of the fixed-blade cutting elements 31comprises a polycrystalline diamond layer or table on a rotationallyleading face of a supporting substrate, the diamond layer or tableproviding a cutting face having a cutting edge at a periphery thereoffor engaging the formation. At least a portion of at least one of thefixed cutting elements 31 is located near or at the axial center 15 ofthe bit body 13 and thus is positioned to remove formation material atthe axial center of the borehole (typically, the axial center of the bitwill generally coincide with the center of the borehole being drilled,with some minimal variation due to lateral bit movement duringdrilling). In a 7⅞ inch bit as illustrated, the at least one of thefixed cutting elements 31 has its laterally innermost edge tangent tothe axial center of the bit 11 (as shown in FIG. 8). In any size bit, atleast the innermost lateral edge of the fixed-blade cutting element 31adjacent the axial center 15 of the bit should be within approximately0.040 inches of the axial center 15 of the bit (and, thus, the center ofthe borehole being drilled).

Fixed-blade cutting elements 31 radially outward of the innermostcutting element 31 are secured along portions of the leading edge ofblade 19 at positions up to and including the radially outermost or gagesurface of bit body 11. In addition to fixed-blade cutting elements 31including polycrystalline tables mounted on tungsten carbide substrates,such term as used herein encompasses thermally stable polycrystallinediamond (TSP) wafers or tables mounted on tungsten carbide substrates,and other, similar superabrasive or super-hard materials such as cubicboron nitride and diamond-like carbon. Fixed-blade cutting elements 31may be brazed or otherwise secured in recesses or “pockets” on eachblade 19 so that their peripheral or cutting edges on cutting faces arepresented to the formation.

Four nozzles 63, 65 are generally centrally located in receptacles inthe bit body 13. A pair of fixed blade nozzles 63 is located close orproximal to the axial center 15 of the bit 11. Fixed blade nozzles 63are located and configured to direct a stream of drilling fluid from theinterior of the bit to a location at least proximate (preferably forwardof to avoid unnecessary wear on elements 31 and the material surroundingand retaining them) at least a portion of the leading edge of each fixedblade 19 and the fixed-blade cutting elements 31 carried thereon (FIGS.4 and 5). Another pair of rolling cutter nozzles 65 are spaced-apartfrom the central axis 15 of the bit boy 13 (radially outward of fixedblade nozzles 63) and are located and configured to direct a stream ofdrilling fluid to a location at least proximate the trailing side ofeach rolling cutter 21 and rolling-cutter cutting elements 25 (FIGS. 4and 5). The streams of drilling fluid cool the cutting elements andremove cuttings from blades 19 and rolling cutters 21 and theirassociated cutting elements 25, 31. Nozzles 63, 65 may be conventionalcylinders of tungsten carbide or similar hard metal that have circularapertures of selected dimension. Nozzles 63, 65 are threaded to retainthem in their respective receptacles. Nozzles 63, 65 may also take theform of “ports” that are integrally formed at the desired location andwith the correct dimension in the bit body 13.

In connection with the nozzles, a pair of junk slots 71 are providedbetween the trailing side of each rolling cutter 21, and the leadingedge of each fixed blade 19 (leading and trailing again are defined withreference to the direction of rotation of the bit 11). Junk slots 71provide a generally unobstructed area or volume for clearance ofcuttings and drilling fluid from the central portion of the bit 11 toits periphery for return of these materials to the surface. As shown inFIGS. 2, 4 and 5, junk slots 71 are defined between the bit body 13 andthe space between the trailing side of each cutter 21 and the leadingedge of each blade 19. The volume of the junk slot exceeds the openvolume of other areas of the bit, particularly in the angular dimension73 of the slot, which is much larger than the angular dimension (andvolume defined) between the trailing edge of each blade 19 and theleading edge of each rolling cutter 21. The increased volume of junkslots 71 is partially accomplished by providing a recess in the trailingside of each fixed blade 19 (see FIG. 1) so that the rolling cutters 21can be positioned closer to the trailing side of each fixed blade thanwould be permitted without the clearance provided by the recess.

Also provided on each fixed blade 19, between the leading and trailingedges, are a plurality of backup cutters or cutting elements 81 arrangedin a row that is generally parallel to the leading edge of the blade 19.Backup cutters 81 are similar in configuration to fixed blade cutters orcutting elements 31, but may be smaller in diameter or more recessed ina blade 19 to provide a reduced exposure above the blade surface thanthe exposure of the primary fixed-blade cutting elements 31 on theleading blade edges. Alternatively, backup cutters 81 may compriseBRUTE™ cutting elements as offered by the assignee of the presentinvention through its Hughes Christensen operating unit, such cuttersand their use being disclosed in U.S. Pat. No. 6,408,958, which isincorporated herein by specific reference. As another alternative,rather than being active cutting elements similar to fixed blade cutters31, backup cutters 81 could be passive elements, such as round or ovoidtungsten carbide or superabrasive elements that have no cutting edge(although still referred to as backup cutters or cutting elements). Suchpassive elements would serve to protect the lower surface of each blade19 from wear.

Preferably, backup cutters 81 are radially spaced along the blade 19 toconcentrate their effect in the nose, shoulder, and gage areas (asdescribed below in connection with FIG. 8). Backup cutters 81 can bearranged on blades 19 to be radially “aligned” with fixed blade cutters31 so that the backup cutters 81 cut in the same groove or kerf made bythe fixed blade cutters 31 on the same blade 19. Alternatively, backupcutters 81 can be arranged to be radially offset from the fixed bladecutters 31 on the same blade 19, so that they cut between the groovesmade by cutters 31. Backup cutters 81 add cutting elements to thecutting profile (FIG. 1) and increase cutter “coverage” in terms ofredundancy at each radial position on the bottom of the borehole.Whether active cutting elements as illustrated or passive elements,backup cutters 81 can help reduce wear of and damage to cutting elements31, and well as reduce the potential for damage to or wear of fixedblades 19. Additionally, backup cutters 81 create additional points ofengagement between bit 11 and the formation being drilled. This enhancesbit stability, for example making the two-fixed-blade configurationillustrated exhibit stability characteristics similar to a four-bladedfixed-cutter bit.

In addition to backup cutters 81, a plurality of wear-resistant elements83 are present on the gage surface at the outermost periphery of eachblade 19 (FIGS. 1 and 2). These elements 83 may be flat-topped orround-topped tungsten-carbide or other hard-metal inserts interferencefit into apertures on the gage surface of each blade 19. The primaryfunction of these elements 83 is passive and is to resist wear of theblade 19. In some applications, it may be desirable to place activecutting elements on the bit leg, such as super-hard (polycrystallinediamond) flat-topped elements with a beveled edge for shear-cutting thesidewall of the borehole being drilled.

FIGS. 6 and 7 illustrate each of the rolling cutters 21, which are ofdifferent configuration from one another, and neither is generallyconical, as is typical of rolling cutters used in rolling-cutter-typebits. Cutter 91 of FIG. 6 has four surfaces or lands on which cuttingelements or inserts are located. A nose or innermost surface 93 iscovered with flat-topped, wear-resistant inserts or cutting elements. Asecond surface 95 is conical and of larger diameter than the first 91,and has chisel-shaped cutting elements on it. A third surface 97 isconical and of smaller diameter than the second surface 95 and again haschisel-shaped inserts. A fourth surface 99 is conical and of smallerdiameter than the second 95 and third 97 surfaces, but is larger thanthe first 93. Fourth surface 99 has round-topped inserts or cuttingelements that are intended primarily to resist wear.

Cutter 101 of FIG. 7 also has four surfaces or lands on which cuttingelements are located. A nose or first surface 103 has flat-topped,wear-resistant cutting elements on it. A second surface 105 is conicaland of larger diameter than the first surface 103. Second surface 105has chisel-shaped cutting elements on it. A third surface 107 isgenerally cylindrical and of larger diameter than second surface 105.Again, chisel-shaped cutting elements are on the third surface 107. Afourth surface 109 is conical and of smaller diameter than third surface107. Round-topped wear-resistant inserts are placed on fourth surface109.

FIG. 8 is a schematic superimposition of the cutter and fixed cuttingelements 25, 31 on each of the cutters and blades obtained by rotatingthe elements about the central axis 15 into a single plane. FIG. 8 isknown as a “cutting profile.” As shown in FIG. 8, the rolling-cuttercutting elements 25 and the fixed-blade cutting elements 31 combine todefine a cutting profile 41 that extends from the axial center 15through a “cone region,” a “nose region,” and a “shoulder region” (seeFIG. 9) to a radially outermost perimeter or gage surface 43 withrespect to the axis (backup cutters 81 are not shown for clarity). Inthe illustrated embodiment, only the fixed-blade cutting elements 31form the cutting profile 41 at the axial center 15 and the gage surface43. However, the rolling-cutter cutting elements 25 overlap or combinewith the fixed-blade cutting elements 31 on the cutting profile 41 toproduce substantially congruent surfaces or kerfs in the formation beingdrilled between the cone region near the axial center 15 and the gageregion at the gage of the borehole 43. The rolling-cutter cuttingelements 25 thus are configured to cut at the nose 45 and shoulder 47 ofthe cutting profile 41, where the nose 45 is the axially leading part ofthe profile (i.e., located between the axial center 15 and the shoulder47) facing the borehole wall and located adjacent the gage surface 43.In this context, “shoulder” is used to describe the transition betweenthe nose region 45 and the gage region and the cutting profile.

FIG. 9 is a superimposition of the cutting profile of FIG. 8 (noted bycurved line 141) with a representative profile generated by a similarlysized (7⅞ inch) three-cone rolling cutter bit (noted by the curved line151). The two profiles are aligned at gage 133, that is, the radiallyoutermost surfaces of each bit are aligned for comparison. The profileof the hybrid bit according to the present invention divides into threeregions, as alluded to previously: a generally linear cone region 143extending from the axial center radially outward; a nose region 141 thatis curved at a selected radius and defines the leading portion of thebit; and a shoulder region 147 that is also curved at a selected radiusand is connects the nose region to the gage of the bit 133. The coneregion 141 describes an angle α with the horizontal bottom of theborehole of between about 10 and 30 degrees, preferably about 20degrees. The selected radii in the nose 145 and shoulder 147 regions maybe the same (a single radius) or different (a compound radius). Ineither case, the profile curve of the hybrid bit is tangent to gage 133at the point at which it intersects the gage. As can be seen, therolling cutter profile 151 defines a generally sweeping curve (typicallyof multiple compound radii) that extends from the axial center to thegage and is not tangent to gage 133 where it intersects gage. The curvedescribed by the profile of the hybrid bit according to the presentinvention thus more resembles that of a typical modern fixed-cutterdiamond bit than that of a rolling-cutter bit.

As illustrated and previously mentioned, the radially innermostfixed-blade cutting element 31 preferably is substantially tangent tothe axial center 15 of the bit 11. The radially innermost lateral orperipheral portion of the innermost fixed cutting element shouldpreferably be no more than 0.040 inch from the axial center 15. Theradially innermost rolling-cutter cutting element 25 (other than thecutter nose elements, which do not actively engage the formation), isspaced apart a distance 29 of about 2.28 inch from the axial center 15of the bit for the 7⅞ inch bit illustrated.

Thus, the rolling-cutter cutting elements 25 and the fixed-blade cuttingelements 31 combine to define a congruent cutting face in the nose 45and shoulder 47 (FIG. 8), which are known to be the most difficult todrill portions of a borehole. The nose or leading part of the profile isparticularly highly loaded when drilling through transitions from softto hard rock when the entire bit load can be concentrated on this smallportion of the borehole. The shoulder, on the other hand, absorbs thelateral forces, which can be extremely high during dynamic events suchas bit whirl, and stick-slip. In the nose and shoulder area, the cuttingspeed is the highest and more than half the cuttings volume is generatedin this region. The rolling-cutter cutting elements 25 crush and pre- orpartially fracture formation in the highly stressed nose and shouldersections, easing the burden on fixed blade cutter elements 31.

A reference plane 51 (FIGS. 2 and 3) is located at the leading ordistal-most axial end of the hybrid drill bit 11. At least one of eachof the rolling-cutter cutting elements 25 and the fixed cutting elements31 extend in the axial direction at the reference plane 51 at asubstantially equal dimension, but are radially offset from each other.However, such alignment in a common plane 51 perpendicular to thecentral axis 15 between the distal-most elements rolling and fixedcutter cutting elements 25, 31 is not required such that elements 25, 31may be axially spaced apart (or project a different distance) by asignificant distance (0.125 inch) when in their distal-most position.The fixed-blade cutting elements 31 are axially spaced apart from anddistal from (e.g., lower than) the bit body 13.

In another embodiment, rolling-cutter cutting elements 25 may extendbeyond (e.g., by approximately 0.060-0.125 inch) the distal-mostposition of the fixed blades 19 and fixed-blade cutting elements 31 tocompensate for the difference in wear between those components. As theprofile 41 transitions from the shoulder 47 to the gage 43 of the hybridbit 11, the rolling-cutter elements 25 no longer engage the formation(see FIG. 8), and multiple rows of vertically-staggered (i.e., axially)fixed-blade cutting elements 31 ream out a smooth borehole wall.Rolling-cutter cutting elements 25 are much less efficient in reaming atthe gage and can cause undesirable borehole wall damage. Indeed, boththe portion of each bit leg 17 above the rolling cutter and the rollingcutters 21 themselves are radially spaced-apart from the sidewall of theborehole so that contact between rolling-cutter cutting elements 25 andthe sidewall of the borehole is minimized or eliminated entirely.

The invention has several advantages and includes providing a hybriddrill bit that cuts at the center of the hole solely with fixed cuttingelements and not with rolling cutters. The fixed-blade cutting elementsare highly efficient at cutting the center of the hole. Moreover, due tothe relatively low cutting velocity of the fixed-blade cutting elementsin the center due to their proximity to the central axis of the bitbody, the polycrystalline diamond compact or other superabrasive cuttingelements are subject to little or no wear. The rolling cutters and theircutting elements are configured to cut a nearly congruent surface (withthe cutting elements on the fixed blade) and thereby enhance the cuttingaction of the blades in the most difficult to drill nose and shoulderareas, which are the leading profile section (axially speaking) and thusare subjected to high wear and vibration damage in harder, more abrasiveformations. The crushing action of the tungsten carbide rolling cutterinserts drives deep fractures into the hard rock, which greatly reducesits strength. The pre- or partially fractured rock is easier to removeand causes less damage and wear to the fixed-blade cutting elements thanpristine formation material commonly drilled by conventional diamond orPDC cutting element-equipped drag bits. The perimeter or gage of theborehole is generated with multiple, vertically-staggered rows offixed-blade cutting elements. This leaves a smooth borehole wall andreduces the sliding and wear on the less wear-resistant rolling cutterinserts.

As discussed above, the fixed-blade cutting elements 31 may includethermally stable polycrystalline diamond (TSP) wafers or tables mountedon tungsten carbide substrates. Alternatively, or additionally, thefixed-blade cutting elements 31 may include mosaic cutters which may beformed of a plurality of geometrically-shaped thermally stable diamondelements cooperatively arranged and bonded in a desired shape, to form aunitary cutting surface. Of course, TSP and/or mosaic fixed-bladecutting elements 31, may be more susceptible to breakage. In any case,in some embodiments, the TSP and/or mosaic fixed-blade cutting elements31 may be similar to any one or more of those shown in the followingUnited States and European patent documents, each of which isincorporated herein be specific reference:

US4664705 US6592985 US7462003 US20060254830 US4726718 US6601662US7473287 US20060266558 US4943488 US6739214 US7493973 US20060266559US5028177 US6749033 US7517589 US20070029114 US5030276 US6797326US7533740 US20070079994 US5116568 US6861098 US7568534 US20070187155US5238074 US6861137 EP157278 US20090114454 US6544308 US6878447 EP2089187US20090178855 US6562462 US7350601 US20050263328 US20090183925 US6585064US7377341 US20060032677 US6589640 US7435478 US20060162969

Therefore, in one embodiment, the rolling cutters 21 may be configuredto act as a depth of cut (DOC) control, or limiter, thereby reducing therisk of damage to the TSP and/or mosaic fixed-blade cutting elements 31.More specifically, the rolling cutters 21 may be positioned, relative tothe fixed blades 19, such that the rolling-cutter cutting elements 25and the fixed-blade cutting elements 31 cooperate up to a maximum DOC,at which point the rolling cutters 21 themselves engage the formation,thereby holding the drill bit 11 back and protecting the TSP and/ormosaic fixed-blade cutting elements 31. As the rolling-cutter cuttingelements 25 and the fixed-blade cutting elements 31 are rotated throughthe formation, they continue to remove formation material, and thereforeallow the drill bit 11 to advance. However, in this embodiment, therolling cutters 21 may be positioned, relative to the fixed blades 19,to prevent excessive rate of penetration (ROP) which may otherwiseexpose the TSP and/or mosaic fixed-blade cutting elements 31 to impactdamage.

For example, rather than the rolling-cutter cutting elements 25 and thefixed-blade cutting elements 31 being aligned at the reference plane 51,as shown in FIG. 2 and FIG. 3, the rolling cutters 21 may be positioned,or may extend, beyond the fixed blades 19, as shown in FIG. 10. In otherwords, the rolling-cutter cutting elements 25 may be positioned, or mayextend, beyond the fixed-blade cutting elements 31, as shown in FIG. 10.More specifically, the rolling cutters 21, themselves, may be aligned atthe reference plane 51, with the rolling-cutter cutting elements 25extending beyond the reference plane 51. Alternatively, the rollingcutters 21 may be positioned, relative to the fixed blades 19, virtuallyanywhere between the alignment shown in FIG. 2 and FIG. 3 and that shownin FIG. 10. In other words, a deepest point of the rolling cutters 21may extend beyond a deepest point of the fixed blades 19, and may or maynot extend beyond a deepest point of the fixed-blade cutting elements31.

Other and further embodiments utilizing one or more aspects of theinventions described above can be devised without departing from thespirit of Applicant's invention. For example, other structures may beused for DOC control and/or prevent excessive ROP, thereby protectingthe TSP and/or mosaic fixed-blade cutting elements 31 from impactdamage. Alternatively and/or additionally, the rolling-cutter cuttingelements 25 may extend beyond the rolling cutters 21 less than thefixed-blade cutting elements 31 extend beyond the fixed blades 19,thereby limiting DOC and/or impact damage to the TSP and/or mosaicfixed-blade cutting elements 31. Of course, the rolling cutter(s) 21 mayinclude few or no rolling-cutter cutting elements 25, and/or may notmeaningfully contribute to ROP other than to act as DOC control and/orprevent excessive ROP, thereby protecting the TSP and/or mosaicfixed-blade cutting elements 31 from damage. Further, the variousmethods and embodiments of the present invention can be included incombination with each other to produce variations of the disclosedmethods and embodiments. Discussion of singular elements can includeplural elements and vice-versa.

The order of steps can occur in a variety of sequences unless otherwisespecifically limited. The various steps described herein can be combinedwith other steps, interlineated with the stated steps, and/or split intomultiple steps. Similarly, elements have been described functionally andcan be embodied as separate components or can be combined intocomponents having multiple functions.

While the invention has been shown or described in only some of itsforms, it should be apparent to those skilled in the art that it is notso limited, but is susceptible to various changes without departing fromthe scope of the invention as hereinafter claimed, and legal equivalentsthereof. The inventions have been described in the context of preferredand other embodiments and not every embodiment of the invention has beendescribed. Obvious modifications and alterations to the describedembodiments are available to those of ordinary skill in the art. Thedisclosed and undisclosed embodiments are not intended to limit orrestrict the scope or applicability of the invention conceived of by theApplicants, but rather, in conformity with the patent laws, Applicantsintend to fully protect all such modifications and improvements thatcome within the scope or range of equivalent of the following claims.

1. An earth boring drill bit comprising: a bit body; a plurality offixed blades extending downwardly from the bit body, each blade having aleading edge and a trailing edge; a plurality of fixed-blade cuttingelements arranged on the leading edge of the fixed blades; at least onerolling cutter mounted for rotation on the bit body; and wherein therolling cutter is configured to act as a depth-of-cut limiter, therebyreducing the risk of damage to the fixed-blade cutting elements.
 2. Thebit as set forth in claim 1, wherein the fixed-blade cutting elementsinclude thermally stable polycrystalline diamond wafers mounted ontungsten carbide substrates.
 3. The bit as set forth in claim 1, whereinthe fixed-blade cutting elements include mosaic cutters formed of aplurality of geometrically-shaped thermally stable diamond elementscooperatively arranged and bonded to form a unitary cutting surface. 4.The bit as set forth in claim 1, wherein the rolling cutter ispositioned, relative to the fixed blades, such that a plurality ofrolling-cutter cutting elements and the fixed-blade cutting elementscooperate up to a maximum depth-of-cut.
 5. The bit as set forth in claim1, wherein the rolling cutter is positioned, relative to the fixedblades, to limit rate of penetration.
 6. The bit as set forth in claim1, wherein the rolling cutter is positioned, relative to the fixedblades, to prevent overexposure of the fixed-blade cutting elements. 7.The bit as set forth in claim 1, wherein the rolling cutter ispositioned, relative to the fixed blades, such that a plurality ofrolling-cutter cutting elements extend beyond the fixed blades.
 8. Thebit as set forth in claim 1, wherein the rolling cutter is positioned,relative to the fixed blades, such that a plurality of rolling-cuttercutting elements extend beyond the fixed-blade cutting elements.
 9. Thebit as set forth in claim 1, wherein the rolling cutter is aligned withthe fixed-blade cutting elements.
 10. The bit as set forth in claim 1,wherein the rolling cutter is aligned between the fixed blades and thefixed-blade cutting elements.
 11. An earth boring drill bit comprising:a bit body; a plurality of fixed blades extending downwardly from thebit body, each blade having a leading edge and a trailing edge; aplurality of fixed-blade cutting elements arranged on the leading edgeof the fixed blades; at least one rolling cutter mounted for rotation onthe bit body; and wherein the rolling cutter is configured to act as arate of penetration limiter, thereby reducing the risk of damage to thefixed-blade cutting elements.
 12. The bit as set forth in claim 11,wherein the fixed-blade cutting elements include thermally stablepolycrystalline diamond wafers mounted on tungsten carbide substrates.13. The bit as set forth in claim 11, wherein the fixed-blade cuttingelements include mosaic cutters formed of a plurality ofgeometrically-shaped thermally stable diamond elements cooperativelyarranged and bonded to form a unitary cutting surface.
 14. The bit asset forth in claim 11, wherein the rolling cutter is positioned,relative to the fixed blades, such that a plurality of rolling-cuttercutting elements and the fixed-blade cutting elements cooperate up to amaximum depth-of-cut.
 15. The bit as set forth in claim 11, wherein therolling cutter is positioned, relative to the fixed blades, to preventoverexposure of the fixed-blade cutting elements.
 16. The bit as setforth in claim 11, wherein the rolling cutter is positioned, relative tothe fixed blades, such that a plurality of rolling-cutter cuttingelements extend beyond the fixed blades.
 17. The bit as set forth inclaim 11, wherein the rolling cutter is positioned, relative to thefixed blades, such that a plurality of rolling-cutter cutting elementsextend beyond the fixed-blade cutting elements.
 18. The bit as set forthin claim 11, wherein the rolling cutter is aligned with the fixed-bladecutting elements.
 19. The bit as set forth in claim 11, wherein therolling cutter is aligned between the fixed blades and the fixed-bladecutting elements.
 20. An earth boring drill bit comprising: a bit body;a plurality of fixed blades extending downwardly from the bit body, eachblade having a leading edge and a trailing edge; a plurality offixed-blade cutting elements arranged on the leading edge of the fixedblades, wherein the fixed-blade cutting elements include thermallystable polycrystalline diamond elements mounted on tungsten carbidesubstrates; at least one rolling cutter mounted for rotation on the bitbody; a plurality of rolling-cutter cutting elements arranged on therolling cutter; and wherein the rolling-cutter cutting elements arepositioned, relative to the fixed-blade cutting elements, to limitdepth-of-cut, rate of penetration, and exposure of the fixed-bladecutting elements, thereby reducing the risk of damage to the fixed-bladecutting elements.